1. Field of the Invention
This invention relates to chimeric and humanized antibodies that specifically bind the BCR complex, and particularly chimeric and humanized antibodies to the BCR complex. The invention also relates to methods of using the antibodies and compositions comprising them in the diagnosis, prognosis and therapy of diseases such as cancer, autoimmune diseases, inflammatory disorders, and infectious disease.
2. Description of the Related Art
The B Cell Receptor (BCR) & The BCR Complex
B cells are immune system cells that are responsible for producing antibodies. The B cell response to antigen is an essential component of the normal immune system. B cells possess specialized cell surface receptors (B cell receptors; “BCR”). If a B cell encounters an antigen capable of binding to that cell's BCR, the B cell will be stimulated to proliferate and produce antibodies specific for the bound antigen. To generate an efficient response to antigens, BCR-associated proteins and T cell assistance are also required. The antigen/BCR complex is internalized, and the antigen is proteolytically processed. A small part of the antigen remains complexed with major histocompatability complex-II (“MHCII”) molecules on the surface of the B cells where the complex can be recognized by T cells. T cells activated by such antigen presentation secrete a variety of lymphokines that induce B cell maturation.
Signaling through the BCR plays an important role in the generation of antibodies, in autoimmunity, and in the establishment of immunological tolerance (Gauld et al. (2002) Science 296(5573):1641-1642) Immature B cells that bind self-antigens while still in the bone marrow are eliminated by apoptosis. In contrast, antigen binding on mature B cells results in activation, proliferation, anergy and apoptosis. The particular functional response observed depends upon whether the B cell receives co-stimulatory signals through other surface receptors and the specific signal transduction pathways that are activated.
The BCR is composed of a membrane immunoglobulin which, together with noncovalently associated α and β subunits of CD79 (“CD79a” and “CD79b,” respectively), forms the BCR complex. CD79a and CD79b are signal transducing subunits that contain a conserved immunoreceptor tyrosine-based activation motif (“ITAM”) required for signal transduction (Dylke et al. (2007) Immunol Lett. 112(1):47-57; Cambier (1995) Immunol Today 16:110). Aggregation of the BCR complex by multivalent antigen initiates transphosphorylation of the CD79a and CD79b ITAMs and activation of receptor-associated kinases (DeFranco (1997) Curr. Opin. Immunol 9:296-308; Kurosaki (1997) Curr. Opin. Immunol 9:309-318; Kim et al. (1993) Immun. Rev. 132:125-146). Phosphorylated ITAMs recruit additional effectors such as PI3K, PLC-γ and members of the Ras/MAPK pathway. These signaling events are responsible for both the B cell proliferation and increased expression of activation markers (such as MHCII and CD86) that are required to prime B cells for their subsequent interactions with T-helper (“Th”) cells.
CD79 expression is restricted to B cells and is expressed in Non-Hodgkin's Lymphoma cells (NHLs) (Olejniczak et al. (2006) Immunol Invest. 35:93-114; D'Arena et al. (2000) Am. J. Hematol. 64:275-281; Cabezudo et al. (1999) Haematologica 84:413-18). CD79a and CD79b and soluble immunoglobulins (“sIg”) are all required for surface expression of the CD79. The average surface expression of CD79b on NHLs is similar to that observed on normal B-cells, but with a greater range (Matsuuchi et al. (2001) Curr. Opin. Immunol 13(3):270-277). CD79b expression in chronic lymphocytic leukaemia cells correlates with mutations in the immunoglobulin heavy chain gene, but does not appear to serve as an independent predictor of clinical severity (Cajiao et al. (2007) Am J. Hematol. 82(8):712-720). Both CD79a and CD79b are involved in antigen-independent (tonic) and antigen-dependent signaling by the BCR (Fuentes-Pananá et al. (2006) J. Immunol. 177(11):7913-7922).
Antibodies that bind to the BCR complex (“Anti-BCR complex antibodies”) have been shown to disrupt BCR signaling, either by causing dissociation of the BCR, or by suppressing (down-regulating) BCR function (see, e.g., U.S. Pat. No. 6,503,509; Polson et al. (2007) Blood 110(2):616-623; Zhang et al. (1995) Ther. Immunol 2(4):191-202). Suppression is generally more desirable, because it avoids potentially undesirable B cell depletion and resultant side effects. Such anti-BCR complex antibodies have therapeutic use in the treatment of autoimmunity, cancer, inflammatory disease, and transplantation. Nevertheless, since human immune systems attack anti-BCR complex murine antibodies, improved antibodies are desired whose use would elicit a reduced human anti-mouse antibody (“HAMA”) response. Likewise, anti-BCR complex antibodies are desired that would exhibit improved binding affinity, or altered effector function.
Fc Receptors
The interaction of antibody-antigen complexes with cells of the immune system results in a wide array of responses, ranging from effector functions such as antibody-dependent cytotoxicity, mast cell degranulation, and phagocytosis to immunomodulatory signals such as regulating lymphocyte proliferation and antibody secretion. All these interactions are initiated through the binding of the Fc domain of antibodies or immune complexes to Fc receptors, which are specialized cell surface receptors on hematopoietic cells. The diversity of cellular responses triggered by antibodies and immune complexes results from the structural heterogeneity of Fc receptors. Fc receptors share structurally related ligand binding domains which presumably mediate intracellular signaling.
The Fc receptors, members of the immunoglobulin gene superfamily of proteins, are surface glycoproteins that can bind the Fc portion of immunoglobulin molecules. Each member of the family recognizes immunoglobulins of one or more isotypes through a recognition domain on the α chain of the Fc receptor. Fc receptors are defined by their specificity for immunoglobulin subtypes. Fc receptors for IgG are referred to as “FcγR,” for IgE as “FεR,” and for IgA as “FcαR.” Different accessory cells bear Fc receptors for antibodies of different isotype, and the isotype of the antibody determines which accessory cells will be engaged in a given response (Billadeau et al. (2002) J. Clin. Investigat. 2(109):161-81; Gerber et al. (2001) Microbes Infection 3:131-139; Ravetch et al. (2001) Annu. Rev. Immunol 19:275-90; Ravetch et al. (2000) Science 290:84-89; Ravetch (1994) Cell 78(4):553-560; Ravetch et al. (1991) Annu. Rev. Immunol 9:457-492; see also, Immunobiology: The Immune System in Health and Disease (4th ed. 1999), Elsevier Science Ltd/Garland Publishing, New York). An overview of various receptors is presented in Table 1.
TABLE 1Receptors for the Fc Regions of Immunoglobulin IsotypesReceptorBindingCell TypeEffect of LigationFcγRIIgG1MacrophagesUptake(CD64)108 M−1NeutrophilsStimulationEosinophilsActivation of respiratory burstDendritic cellsInduction of killingFcγRII-AIgG1MacrophagesUptake(CD32)2 × 106 M−1NeutrophilsGranule releaseEosinophilsDendritic cellsPlateletsLangerhan cellsFcγRII-B1IgG1B cellsNo uptake(CD32)2 × 106 M−1Mast cellsInhibition of StimulationFcγRII-B2IgG1MacrophagesUptake(CD32)2 × 106 M−1NeutrophilsInhibition of StimulationEosinophilsFcγRIIIIgG1NK cellsInduction of Killing(CD16)5 × 105 M−1EosinophilsMacrophagesNeutrophilsMast CellsFcεRIIgEMast cellsSecretion of granules1010 M−1EosinophilBasophilsFcαRIIgA1, IgA2MacrophagesUptake(CD89)107 M−1NeutrophilsInduction of killingEosinophils
Each Fcγ receptor (“FcγR”) is an integral membrane glycoprotein, possessing extracellular domains related to a C2-set of immunoglobulin-related domains, a single membrane spanning domain and an intracytoplasmic domain of variable length. There are four known FcγRs, designated FcγRI (CD64), FcγRII (CD32), FcγRIII (CD16), and FcγRIV. The receptors are encoded by distinct genes; however, the extensive homology between the family members suggest they arose from a common progenitor perhaps by gene duplication.
Both activating and inhibitory signals are transduced through the FcγRs following ligation. These diametrically opposing functions result from structural differences among the different receptor isoforms. Two distinct domains within the cytoplasmic signaling domains of the receptor called immunoreceptor tyrosine based activation motifs (ITAMs) or immunoreceptor tyrosine based inhibitory motifs (ITIMS) account for the different responses. The recruitment of different cytoplasmic enzymes to these structures dictates the outcome of the FcγR-mediated cellular responses. ITAM-containing FcγR complexes include FcγRI, FcγRIIA, FcγRIIIA, and FcγRIV, whereas ITIM-containing complexes only include FcγRIIB.
FcγRI displays high affinity for the antibody constant region and restricted isotype specificity (Hulett and Hogarth (1994) Adv Immunol 57:1-127). FcγRII proteins are 40 KDa integral membrane glycoproteins which bind only the complexed IgG due to a low affinity for monomeric Ig (106 M−1). This receptor is the most widely expressed FcγR, present on all hematopoietic cells, including monocytes, macrophages, B cells, NK cells, neutrophils, mast cells, and platelets. FcγRII has only two immunoglobulin-like regions in its immunoglobulin binding chain and hence a much lower affinity for IgG than FcγRI. There are three known human FcγRII genes (FcγRII-A, FcγRII-B, FcγRII-C), all of which bind IgG in aggregates or immune complexes. Human neutrophils express the FcγRIIA gene. The FcγRIIB gene is expressed on B lymphocytes; its extracellular domain is 96% identical to FcγRIIA and binds IgG complexes in an indistinguishable manner.
Distinct differences within the cytoplasmic domains of FcγRII-A and FcγRII-B create two functionally heterogenous responses to receptor ligation. The FcγRII-A isoform initiates intracellular signaling leading to cell activation such as phagocytosis and respiratory burst, whereas the FcγRII-β isoform initiates inhibitory signals, e.g., inhibiting B-cell activation. FcγRIIA clustering via immune complexes or specific antibody cross-linking serves to aggregate ITAMs along with receptor-associated kinases which facilitate ITAM phosphorylation. ITAM phosphorylation serves as a docking site for Syk kinase, activation of which results in activation of downstream substrates (e.g., PI3K). Cellular activation leads to release of proinflammatory mediators. When co-ligated or co-aggregated along with an activating FcγR having an ITAM, such as FcγRIIA or FcεRI, the ITIM in FcγRIIB becomes phosphorylated and recruits the SH2 domain of the src homology 2-containing inositol phosphatase (SHIP), which in turn is phosphorylated and associates with Shc (Ott (2002) J. Immunol. 162(9):4430-4439; Yamanshi et al. (1997) Cell 88:205; Carpino et al. (1997) Cell 88:197). SHIP hydrolyzes phosphoinositol messengers released as a consequence of ITAM-containing FcγR-mediated tyrosine kinase activation, consequently preventing the influx of intracellular Ca++, and dampening cellular responsiveness to FcγR ligation. Thus, B cell activation, B cell proliferation and antibody secretion is aborted, and FcγR-mediated phagocytosis is down-regulated (Tridandapani et al. (2002) J. Biol. Chem. 277(7):5082-89).
Specifically, coaggregation of FcγRIIA with FcγRIIB results in down-regulation of phosphorylation of Akt, which is a serine-threonine kinase that is involved in cellular regulation and serves to suppress apoptosis, and coaggregation of FcγRIIB with the high affinity IgE receptor FcεRI in mast cells leads to inhibition of antigen-induced degranulation, calcium mobilization, and cytokine production (Long (1999) Annu Rev. Immunol 17:875; Metcalfe et al. (1997) Physiol. Rev. 77:1033). Coaggregation of FcγRIIB and the B-cell receptor (BCR) leads to inhibition of BCR-mediated signaling, and inhibition of cell cycle progression and cellular survival. Although numerous effector functions of FcγRIIB-mediated inhibition of BCR signaling are mediated through SHIP, recently it has been demonstrated that lipopolysaccharide (LPS)-activated B cells from SHIP deficient mice exhibit significant FcγRIIB-mediated inhibition of calcium mobilization, Ins(1,4,5)P3 production, and Erk and Akt phosphorylation (Brauweiler et al. (2001) Journal of Immunology 167(1): 204-211).
The size of FcγRIII ranges between 40 and 80 kDa in mouse and man, due to heterogeneity within this class. Two human genes encode two transcripts, FcγRIIIA, an integral membrane glycoprotein, and FcγRIIIB, a glycosylphosphatidyl-inositol (GPI)-linked version. One murine gene encodes an FcγRIII homologous to the membrane spanning human FcγRIIIA. The FcγRIII shares structural characteristics with each of the other two FcγRs. Like FcγRII, FcγRIII binds IgG with low affinity and contains the corresponding two extracellular Ig-like domains. FcγRIIIA is expressed in macrophages, mast cells, and is the lone FcγR in NK cells. The GPI-linked FcγRIIIB is currently known to be expressed only in human neutrophils.
FcγRIV (also known as mFcRIV) requires association of the FcR gamma-chain for optimal expression and function on myeloid cells; its signaling potential is also enhanced by a cytoplasmic “YEEP” motif that recruits the adaptor molecule Crk-L and phosphatidylinositol-3-OH kinase. FcγRIV preferentially binds immunoglobulin E antibodies of the b allotype (IgEb) as well as IgG2a and IgG2b antibodies. Ligation of FcγRIV by antigen-IgEb immune complexes promotes macrophage-mediated phagocytosis, presentation of antigen to T cells, production of proinflammatory cytokines and the late phase of cutaneous allergic reactions (Hirano et al. (2007) Nature Immunology 8:762-771). FcγRIV is a recently identified receptor, conserved in all mammalian species with intermediate affinity and restricted subclass specificity (Nimmerjahn et al. (2005) Immunity 23:41-51; Mechetina et al. (2002) Immunogenetics 54:463-468; Davis et al.
(2002) Immunol Rev 190:23-36). FcγRIII and FcγRIV are physiologically important activation FcγRs for mediating inflammatory disease triggered by cytotoxic antibodies or pathogenic immune complexes. FcγRIV is found on dendritic cells, macrophages, monocytes and neutrophils.
Despite all such advances, a need remains for anti-BCR complex antibodies that possess therapeutic use in the treatment of autoimmunity, cancer, inflammatory disease, and/or transplantation, and exhibit improved ability to mediate effector function from the Fc receptors. The present invention is directed to this and other needs.